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Plate Tectonics theory that describes the formation, movement, and interactions of lithosphere sections that move over the athenosphere Updated Created by C. Ippolito April 2009 Early Ideas About Plate Movements • 1596 – Dutch mapmaker suggested Africa and South America may have been one continent • 1912 Alfred Wegener – Continental Drift • hypothesis that continents had drifted or moved – Mesosaurus found eastern S.A. & western Africa – rock formations matchup • Pangea – single “super continent” Updated Created by C. Ippolito April 2009 Permian Era (225 mya) Updated Created by C. Ippolito April 2009 Triassic (200 mya) Updated Created by C. Ippolito April 2009 Jurassic (135 mya) Updated Created by C. Ippolito April 2009 Cretaceous (65 mya) Updated Created by C. Ippolito April 2009 Present Day Updated Created by C. Ippolito April 2009 Theory of Plate Tectonics • Capt. H. H. Hess – believed Wegener – echo soundings of ocean floor • mapped midocean ridges – younger rocks at “rifts” – older rocks on sides – presented sea floor spreading mechanism (1960’s) – located deep sea trenches • continental mtns (Andes) • island arcs (Japan, Aleutians) Updated Created by C. Ippolito April 2009 Other Evidence for Plate Tectonic Theory • • • • Updated Worldwide distribution of volcanoes Worldwide distribution of earthquakes Age of rocks at rifts Paleomagnetic “stripes” are symmetrical about ridges – confirming seafloor spreading Created by C. Ippolito April 2009 Basic Concepts • Lithosphere (upper mantle + crust) – made of rigid plates • Plates move slowly • Geologic activity at or near boundaries • Interior of plates “quiet” Updated Created by C. Ippolito April 2009 Types of Plate Boundaries • Divergent Boundary – move away from each other • Convergent Boundary – move toward each other • Transform Boundary – move past each other Updated Created by C. Ippolito April 2009 Divergent Boundary • plates move apart – mantle convection • Mid Atlantic Ridge • East Pacific Rise Updated Created by C. Ippolito April 2009 Convergent Boundary • plates moving toward each other – Subduction Boundary • one plate moves under the other – ocean-ocean » deep sea trenches » island arcs – ocean-continent » coastal volcanoes – Collision Boundary • plates push against each other form mtns – continent-continent » Himalays Updated Created by C. Ippolito April 2009 Transform Boundary • plates slide past each other – earthquake activity • San Andreas Fault • North Anatolian Fault (Turkey) Updated Created by C. Ippolito April 2009 Causes of Plate Movement • Mantle Convection – Magma hotter and less dense at ridge – As it rises and moves away it pulls plate • Ridge Push – New formed rock cools/is more dense – Gravity has it “slide” away from ridge • Slab Pull – At subduction zone denser plate “pulls down” Updated Created by C. Ippolito April 2009
